In an optical transmission system, a device that multiplexes signals transmitted via a plurality of lanes and transmits a multiplexed signal via one lane is in practical use. For example, in a network illustrated in FIG. 1, a node device 100 multiplexes client signals transmitted from a plurality of clients C1-C4 and transmits a multiplexed signal to a metro system network.
In a long-distance trunk system, the Multi-Lane Distribution (MLD) that is performed in an Optical Transport Network (OTN) is known. In the Multi-Lane Distribution, a skew between parallel signals is adjusted, and a serial transmission signal is generated. However, in an access system network and/or the metro system network, a configuration simpler than the Multi-Lane Distribution of the OTN is requested in some cases.
FIG. 2 illustrates an example of a conventional optical transceiver. The optical transceiver illustrated in FIG. 2 transmits an optical signal of 100 Gbps obtained by multiplexing ten data signals of 10 Gbps. In addition, the optical transceiver reproduces the ten data signals of 10 Gbps from the received optical signal of 100 Gbps. Each of the data signals of 10 Gbps is, for example, a 10 GbE signal. The optical signal of 100 Gbps is, for example, a 100 GbE signal.
A gear box converts a transmission speed and the number of transmission lanes in an electric domain. For example, a gear box 201 converts ten input lanes into four intermediate lanes. In this case, each of the input lanes transmits a 10 Gbos data signal, and each of the intermediate lanes transmits a 25 Gbps signal. Each transmitter Tx converts a signal of a corresponding one of the intermediate lanes into an optical signal. Wavelengths (λ1-λ4) of the optical signals generated by the respective transmitters Tx are different from each other. Then, an optical multiplexer multiplexes a plurality of optical signals and generates a 100 Gbps optical signal. The 100 Gbps optical signal is a WDM optical signal. An optical demultiplexer demultiplexes the 100 Gbps optical signal for each wavelength. Each receiver Rx converts a corresponding optical signal obtained by the optical demultiplexer into an electric signal. Each of the electric signals is guided to a gearbox 202 via the intermediate lane. Then, the gear box 202 converts the four intermediate lanes into ten output lanes. As a result, the 10 Gbps data signals are transmitted to respective clients.
FIG. 3 illustrates an example of a configuration of an optical transmission system using an OFDM (Orthogonal Frequency Division Multiplexing) base intensity modulation scheme. In a transmitter of the optical transmission system, user data is converted into an OFDM signal by a modulator (mapper), an inverse Fourier transformer (IFFT), a serializer, and a D/A converter. An optical OFDM signal is generated by driving a light source by the OFDM signal. The optical OFDM signal is transmitted via an optical fiber. In a receiver, the optical OFDM signal is converted into an electric signal. Then, the user data is reproduced from the electric signal by an A/D converter, a deserializer, a Fourier transformer (FFT), and a demodulator (demapper). In the OFDM, data is transmitted using a plurality of sub-carriers.
A technique relating to the optical OFDM is described in, for example, Non-Patent Document 1. In addition, Non-Patent Document 2 describes a relevant technique. Further, Patent Document 1 describes a frame transfer device including a transfer unit, a frame generator, and a multiplex transmitter. The transfer unit transfers in parallel client signals using a plurality of lanes. The frame generator, that is provided in each of the plurality of lanes, accommodates a client signal from the transfer unit in an accommodation frame corresponding to a bit rate of each of the lanes without performing a multi-lane distribution termination process on the client signal. The multiplex transmitter multiplexes a plurality of frames generated by the frame generators, and transmits a multiplexed frame.    Patent Document 1: Japanese Laid-open Patent Publication No. 2010-213184    Non-Patent Document 1: J. L. Wei, et al., “7 dB Optical Power Budget Improvements of 11.25 Gb/s Optical OFDM PON system Using Optical Filters”, OMG1, OFC2011    Non-Patent Document 2: C. Milion, et al., “High Bit Rate Transmission for NG-PON by Direct Modulation of DFB Laser using Discrete Multi-Tone”, Paper 7.5.4, ECOC 2009, 20-24 September, 2009
When a plurality of transmission signals transmitted via a plurality of lanes are multiplexed so as to generate an optical signal, in the conventional technique illustrated in FIG. 2, a gearbox that converts a transmission speed and the number of transmission lanes is used. However, the gear box consumes large power. In addition, the gear box has a large size of circuit
When the optical OFDM illustrated in FIG. 3 is used, in order to multiplex a plurality of transmission signals transmitted via a plurality of lanes so as to generate an optical signal, it is needed that the plurality of transmission signals are converted into serial data signals using a gear box, and the serial data signals are input into an OFDM modem. Therefore, also in this case, the gear box is needed, and therefore the problem of consumption power and/or a circuit size is not solved.